Gravel packing a well reduces the amount of formation sand that is produced with the production fluid. Due to its abrasive nature, formation sand in the production fluid is detrimental to downhole completion equipment and surface production equipment. Gravel packing comprises packing the annulus between the perforated wellbore and slotted screens positioned opposite the perforations on the end of the production tubing with sand or gravel to form a filter for reducing the flow of formation sand into the wellbore.
The predominant methods of conventional gravel packing are the circulating pack and squeeze pack methods. In a circulating gravel pack, the gravel pack slurry is displaced down the tubing string and through the gravel pack assembly to deposit sand or gravel in the perforations and between the perforations in the wellbore and a slotted screen attached to the bottom of the gravel pack assembly. After depositing the gravel pack sand, the carrier fluid of the slurry passes through the slotted screen and is circulated out of the borehole. Circulating gravel packs generally offer the highest chances for success in gravel packing.
The squeeze gravel pack method also deposits the gravel pack sand or gravel in the perforations and between the perforations and the slotted screen but does not provide a means for circulating the carrier fluid out of the wellbore. Instead, the carrier fluid is displaced, or squeezed into the formation through the perforations after the sand or gravel is deposited in the annulus between the perforations and the screen. Ideally, the carrier fluid is removed from the formation after the gravel pack job is completed and the well is returned to production.
Over time, older gravel packs tend to fail or reach a state where repairs are necessary. Corrosion and sand cutting are typical examples of how gravel packs reach a deteriorated state. Ideally, an operator could repair a deteriorated gravel pack instead of replacing the gravel pack. This is especially important in wells where it is economically not feasible to replace the existing gravel pack. The present invention is well-suited for remedial repairs of pre-existing gravel pack completions.
The present invention is designed to allow through-tubing circulating and squeeze packs using a through-tubing gravel pack assembly and surface manipulation of the coiled tubing string. With the present invention, an operator can change "on-the-fly" from circulating to squeeze mode, and vice versa, as many times as necessary as well conditions change. The present invention is directed to a single-trip tool which can perform both circulating and squeeze gravel packs without the necessity of tripping out of the hole for changes to the gravel pack assembly. Thus, the gravel pack assembly is capable of being reciprocated between circulating and squeeze positions while in the hole. A squeeze pack can be performed without having to use the blow-out preventers to close the annulus at the surface. In one embodiment of the invention, a fluid control check valve is utilized in a circulating squeeze which eliminates fluid loss to the formation when the carrier fluid is reversed out of the hole. The invention does not depend upon the presence of seating nipples in the existing tubing string for anchoring the assembly in the well. Furthermore, since the gravel pack assembly of the present invention can be run on coiled tubing string, a gravel pack can be conducted without the necessity of an expensive drilling or completion rig.